Modern turbines often operate at extremely high temperatures. The effect of temperature on the turbine blades and/or stator vanes can be detrimental to the efficient operation of the turbine and can, in extreme circumstances, lead to distortion and possible failure of the blade or vane. In order to overcome this risk, high temperature turbines may include hollow blades or vanes incorporating so-called impingement tubes for cooling purposes.
These so-called impingement tubes are hollow tubes that run radially within the blades or vanes. Air is forced into and along these tubes and emerges through suitable apertures into a void between the tubes and interior surfaces of the hollow blades or vanes. This creates an internal air flow for cooling the blade or vane.
Normally, blades and vanes are made by a casting having hollow structures in which impingement tubes are inserted for impingement cooling of an impingement cooling zone of the hollow structure. Problems arise when a cooling concept is used by which an impingement cooling in downstream regions of the impingement cooling zone is inefficient due to strong cross flow effects.
This is known from a cooling concept, where a large impingement cooling zone is cooled by a single impingement tube or array and cooling medium discharged from the impingement tube flows from a leading edge to a trailing edge of the aerofoil along a flow channel arranged between an aerofoil wall and the impingement tube.